Hirao K, Sato T, Otomo K, Yamamoto N, Nawara H, Doshida N, Suzuki F, Kawara T, Hiejima K, Tanaka M
First Department of Internal Medicine, School of Medicine, Tokyo Medical and Dental University, Japan.
Jpn Circ J. 1994 May;58(5):351-61. doi: 10.1253/jcj.58.351.
To determine the optimal temperature for catheter heat mapping without damaging cardiac tissue, we studied the electrophysiologic and histologic responses of the atrioventricular (AV) conduction system exposed to a specific range of temperatures. In 18 closed-chest dogs, an electrode catheter with a thermistor, tip was positioned transvenously at the AV junction. Radiofrequency current (RFC) was applied in incremental temperature steps until transient 2nd-degree AV block was induced. Catheter tip temperature (CTT) was measured at each step. RFC was immediately discontinued when AV block occurred. AV conduction was evaluated before and 4 weeks after the procedure. Acute transient 2nd-degree AV block was induced in 45 applications, during which the average CTT was 48.7 +/- 2.7 degrees C. In another 40 applications in which 2nd degree AV block was not induced, the average CTT was significantly lower [46.3 +/- 2.5 degrees C] (p < 0.001). Eleven of 16 dogs showed acute 2nd-degree AV block, but had normal AV conduction at 4 weeks (Group A). In the other 5 dogs, 1st-degree AV block was seen at 4 weeks (Group B). The lowest CTTs in Groups A and B were 45 and 49 degrees C, respectively. Histologic findings in 2 dogs from Group A revealed that 10-15% (by area) of the AV node was fibrotic. These findings suggest that the induction of fully reversible AV block can be achieved by titration of RFC, during the application of RFC to the AV junction. In conclusion, RF energy was used to produce a tip temperature of between 45 degrees C and 49 degrees C, which induced reversible and significant interruption of conduction of in tissue in the AV junction, and presumably also in target sites in clinical RF ablation.
为确定在不损伤心脏组织的情况下进行导管热标测的最佳温度，我们研究了房室（AV）传导系统暴露于特定温度范围时的电生理和组织学反应。在18只开胸犬中，将带有热敏电阻尖端的电极导管经静脉置于房室交界处。以递增的温度步长施加射频电流（RFC），直至诱发短暂的二度房室传导阻滞。在每个步骤测量导管尖端温度（CTT）。当发生房室传导阻滞时立即停止RFC。在手术前和术后4周评估房室传导。在45次应用中诱发了急性短暂二度房室传导阻滞，在此期间平均CTT为48.7±2.7℃。在另外40次未诱发二度房室传导阻滞的应用中，平均CTT显著更低[46.3±2.5℃]（p<0.001）。16只犬中有11只出现急性二度房室传导阻滞，但在4周时房室传导正常（A组）。在另外5只犬中，4周时出现一度房室传导阻滞（B组）。A组和B组的最低CTT分别为45℃和49℃。A组2只犬的组织学结果显示，房室结10 - 15%（按面积）发生纤维化。这些结果表明，在向房室交界处施加RFC的过程中，通过滴定RFC可实现完全可逆的房室传导阻滞。总之，射频能量用于产生45℃至49℃之间的尖端温度，这可诱发房室交界处组织传导的可逆性和显著中断，临床射频消融中的靶部位可能也是如此。
